Abstract: A tankless electric water heater having instantaneous hot water output includes an open-ended folded tubular conduit having a separate metal-sheathed immersion heating element inserted in to each end of the conduit and carried by a cap member sealing the open end. Each cap member carries a thermostat having a preset temperature of about 140.degree. F. and connected in series with the heating element carried by the respective cap member. A self-regulating PTC heating cable, either disposed in or wrapped around the tubular conduit, is continuously energized independently of the metal-sheathed heating elements to maintain the water in the tubular conduit a constant temperature of about 150.degree. C. during standby periods.